Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$11.93	12.412%	$13.4108	$13.41	$13.40	$13.40
Purchase #2	$212.38	3.557%	$219.9344	$219.93	$219.95	$219.90
Purchase #3	$90.65	11.435%	$101.0158	$101.02	$101.00	$101.00
Purchase #4	$152.28	4.209%	$158.6895	$158.69	$158.70	$158.70
Purchase #5	$160.27	10.310%	$176.7938	$176.79	$176.80	$176.80
Purchase #6	$215.49	3.719%	$223.5041	$223.50	$223.50	$223.50
Purchase #7	$55.55	7.295%	$59.6024	$59.60	$59.60	$59.60
7 purchase totals =	$898.55		$952.9508	$952.94	$952.95	$952.90